Dual-orifice return flow nozzle



April 1962 w. G. WEBSTER 3,029,029

DUAL-ORIFICE RETURN FLOW NOZZLE Filed May 26, 1959 7 F 55 8- f ,29 2 A 30W 35|l 3| s 5 34 33 5 J3 E SWIRL 3 SWIRL SLOTS INVENTOR.

WILLIAM G. WEBSTER BY INLET FUEL FLOW JW f I D W ATTORNEYS PASSAGES United States atent @hhce 3,629,029 DUAL-ORIFICE RETURN FLOW NOZZLE William G. Webster, Lyndhurst, Ohio, assignor to Parker- Hannifin Corporation, Cleveland, Ohio, a corporation of Ohio Filed May 26, 1959, Ser. No. 815,876 5 Claims. (Cl. 239-404) The present invention relates generally as indicated to a dual-orifice return flow nozzle for use as with a gas turbine power plant.

Basically, fuel injectors or nozzles as presently used in gas turbines may be classified as the simplex, duplex, dualorifice, and spill types. In order that the features and advantages of the present nozzle may be readily comprehended, these known nozzle types will now be generally described.

The simplex nozzle is a single orifice nozzle and is, of course, the simplest and least expensive of those enumerated above. However, the simplex nozzle has the disadvantage that it has a relatively narrow range of useful fuel flow (maximum to minimum) at which the main droplet size is in the fine mist classification (droplet size less than about 150 microns) for achievingefiicient combustion. Following is a table of typical simplex nozzles and their characteristics, assuming 500 p.s.i. as the maximum fuel pressure:

In the simplex nozzle the fixed orifice thereof is what meters the flow of fuel and therefore such nozzle is subject to the square root law i.e., the rate of flow through the orifice is proportional to the square root of the applied fuel pressure, the fuel being admitted under pressure through tangentially directed swirl ports into a conical vortex chamber and acquiring an increasing whirl velocity as the diameter of the chamber decreases. The fuel is discharged from the orifice as a conical spray since it has both axial and tangential velocity components. The vortex chamber and orifice usually do not flow fuel whereby there is an axial core of air or fuel vapor which persists in the base of the vortex chamber. pressures from zero to the minimums appearing in Table I, the fuel discharge from the orifice is first a dribble then a twisted jet and, then as the fuel pressure approaches the minimum, the jet opens out to form a tulip-shaped liquid sheet with some break-up into drops which may be referred to as rain. As the fuel pressure is increased above the minimum the fuel issues from the orifice in the form of a conical spray consisting of a cloud of fine particles.

In order to substantially extend the useful fuel flow range, resort has been made to the other types of nozzles, such as the duplex, dual-orifice, and spill types previously mentioned.

In the duplex nozzle extended useful fuel flow range may be achieved as by providing a sliding piston which forms the large end of the vortex chamber and which moves back against a spring under increasing pressure to thereby increase the swirl port area. Some disadvantages of the duplex nozzle are the necessity of extreme accurate machining of the components, the difiiculty of accurately At the very low fuel 7 matching a set of nozzles, and the diificulty of maintaining adequate sensitivity of the nozzle during the cut-in period of the larger swirl ports whereby the fuel flow may vary widely without a corresponding change in fuel pressure.

The socalled dual-orifice nozzle is in many respects similar to the duplex nozzle, and, as the name dualorifice impl'es, there are usually provided two separate orifices whereby at low pressures and low fuel flows the fuel is discharged through a small or primary orifice whereas at higher pressures and greater rates of fuel flow fuel is discharged additionally through a larger or secondary orifice. While the dual-orifice nozzle gives good atomization over a wide range of useful fuel flow it re quires careful design and matching of individual nozzles to avoid sudden changes in pressure-flow characteristics. The cutin point of the secondary orifice may be controlled as by check valves or by separate fuel manifolds. It has been proposed to employ specially designed flow dividers in an attempt to provide the desired sensitivity of flow to pressure throughout the usefulflow range which may be as great as :1.

The spill type nozzle above referred to has the advantage that it itself has no moving parts and is relatively easy to manufacture, the principle of operation thereof being that fuel .is bled off the vortex chamber in varying amounts as controlled by a valve in the bleed line. Accordingly, a large amount of fuel at high pressure may be admitted into the vortex chamber to produce high whirl energy, but only a desired portion of this fuel is allowed to discharge through the nozzle orifice, The ideal condition of operation ofthis type of nozzle is that of constant inlet pressure with all control being effected by the spill valve thus insuring constant high whirl velocity and hence fine atomization at all flows over a-wide useful range. However, one chief disadvantage of the spill type nozzle is that a pump of relatively large capacity is required since the total flow, that is, the discharge plus the spill may be several times that of the actual output required.

With the foregoing in mind, it is accordingly a principal object of this invention to provide a simple and efficient nozzle which embodies the advantages, but not the disadvantages, of the simplex, dual-orifice and spill type nozzles to provide for Wide useful ranges of fuel flow.

It is another object of this invention to provide a dualorifice return flow nozzle of the character indicated which employs in the secondary orifice flow line a quick opening valve that is opened automatically in response to the inlet fuel pressure reaching a predetermined value, whereafter the valve remains open despite the fact that the inletfuel pressure may subsequently drop down to a value less than such predetermined value.

It is another object of this invention to provide a dualorifice return flow nozzle which is of simple compact form, which is easy and economical to manufacture, and which may be readily disassembled for cleaning or servicing.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however of but one of the various ways in which the principle of the invention may be employed.

In said annexed drawing:

FIG. 1 is a central cross-section view of a dual orifice return flow nozzle according to this invention;

FIG. 2 is a fragmentary cross-section view taken substantially along the line 2'2, FIG. 1;

Patented Apr. 10, 1962' FIG. 3 is a fuel pressure versus inlet fuel flow chart illustrating the preferred characteristics of the pressure actuated valve in the secondary supply line.

Referring now more particularly to the drawing and especially to FIGS. 1 and 2 there is shown therein a nozzle assembly 1 including a body 2 formed with a secondary fuel passage 3 and a spill or bleed passage 4, said passages being disposed in generally side-by-side relation and terminating at their upper ends in counter bores in which are located O-rings 5 and 6 or the like. Secured as by screws (not shown) or the like to the flanged upper end of said body 2 is a cap member 7 formed with a fuel inlet port 8 and with a bleed port 9, the latter being connected to a suitable bleed valve (not shown) such as a needle valve, for example, which is operative to control the rate of flow of fuel through the spill or bleed passage 4 to thus build up a desired back pressure in that passage.

The lower end of the body 2 is formed with an externally threaded leg 10 which is formed with a bore 11 intersecting both the secondary passage 3 and the bleed passage 4. Fitted into said bore 11 and brazed or otherwise secured in place is a nozzle insert 12 which has a peripheral flange 13 that isolates the secondary and bleed passages 3 and 4 from each other. Said insert 12 also has a peripheral groove 14 which communicates with the secondary passage 3, and adjacent such groove, the insert 12 is formed with a peripheral series of grooves 15.

Having threaded engagement with said leg is a nozzle shield 16 which serves to clamp the nozzle orifice cap 17 on leg 10 and the parts 18 and 19 against insert 12. The nozzle cap 17 forms with the parts 18 and 19 a generally conical secondary whirl or vortex chamber 20 through which the fuel is adapted to flow via secondary passage 3, groove 14, grooves 15, and tangential swirl slots 21 in part 18 to acquire progressively increasing tangential velocity as it approaches the secondary discharge orifice 22, said orifice being formed in the nozzle cap 17. The intermediate part 18 is formed with swirl slots 21 as aforesaid so as to impart whirling motion to Elbe fuel as it enters the periphery of the vortex chamber The insert 12 is formed with passages 23 therethrough which lead to the lower end of the spill passage 4 from an annular zone 23' in the base of the secondary swirl chamber 20. As shown, a primary orifice assembly 24 with its swirl slots 25, swirl chamber 26 and primary discharge orifice 27 extends through the nozzle part 19 to a zone just upstream of the secondary orifice 22 whereby the secondary orifice 22 is in essence an annular orifice. The primary discharge orifice assembly 24 has a spider portion 23" as shown whereby any desired portion of the fuel in the secondary swirl chamber 20 may be bled off into the spill passage 4 by way of passages 23 when the spill control valve (not shown) is partway or fully open and, of course, when the spill control valve is closed the entire quantity of fuel flowing through the secondary swirl chamber 20 will be discharged through the secondary orifice 22.

The insert 12 aforesaid is also formed with a central passage 28 through which fuel is supplied by way of a tube 29 which extends through the secondary passage 3 and then is bent as best shown in FIG. 2 to communicate with a primary passage 29' which leads to the fuel inlet port 8 upstream of the spring seated valve 30 in the secondary passage. Thus, the fuel inlet port 8 terminates in a primary branch passage 29 which leads to the primary orifice 27 via swirl slots in assembly 24 and a swirl chamber 26, and in a secondary branch passage 3 which leads to the secondary orifice 22 via swirl slots 21 and a secondary swirl chamber 20.

The primary line 28 registers with the primary passage 29' at the upper flanged end of the body 2 and is sealed with the cap 7 by means of the O-ring 31.

The valve previously referred to is preferably in the form of a spring seated check valve which is adapted to be seated against the seat 32 in the cap 7 by pressure of the spring 33, the spring being backed up as by means of a snap ring 34 or the like. This valve 30 is preferably of a type which has a large differential area on its inlet side whereby once the valve 30 has been urged away from its seat 32 it will readily open by pressure on the secondary area thereof to permit free flow of fuel through the openings 35 thereof and will remain open even though the fuel pressure in inlet port 8 may eventually drop down to a value much less than that which was required to initially open said valve.

Accordingly, when the gas turbine is to be started, the valve 30 is in closed position so that the fuel will fiow only through the primary circuit to the primary orifice 27 so as to provide for fine atomization of the fuel for starting when the inlet flow is low. However, as the turbine accelerates and the inlet flow increases, the valve 30 will be urged away from its seat to allow fuel to flow additionally through the secondary circuit to the secondary orifice 22. Of course, the amount of fuel which is discharged through the secondary orifice 22 will be controlled by the back pressure in the spill or bleed system 4 and 23 which extends from the base of the vortex chamber 20. The pressure actuated valve 30 is designed to be fully closed at the inlet flow corresponding to idling speed of the turbine and under all operating conditions beyond idling, the valve 30 is fully open and the nozzle functions as a return flow or spill type nozzle. Stated in another way, in starting the turbine there is adequate fuel flow, and atomization is provided at low pump speeds because the valve 30 is at that time closed and thus allows flow only to the primary orifice 27. During acceleration after fire-up the inlet pressure increases and opens the valve 30 thus providing normal spill nozzle flow through orifice 22 in addition to the flow through the primary orifice 27. As aforesaid, the valve 30 is designed with a large secondary area (around seat 32) so that the inlet flow under all flight conditions will hold it fully open. This valve 30 is not a variable metering device and does not reseat until the turbine is shut down. Reference may be had to FIG. 3 which shows the pressure versus flow characteristics of valve 30. Thus, while initially the inlet pressure may be of value X to open said valve against the spring pressure, as the inlet fuel flow increases, the pressure through the valve 30 drops to a very low value as at Y whereafter, it becomes more or less a fixed orifice valve which has the previously mentioned square root flow characteristics, but at the low end of the square root curve so as not to impose any substantial restriction to fuel flow at any time, even at the maximum fuel fiow which is shown at Z.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims, or the equivalent of such, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. A dual-orifice return flow nozzle having a fuel inlet passage through which fuel is adapted to How to primary and secondary discharge orifices of said nozzle via primary and secondary branch passages, primary and secondarylswirl slots, and primary and secondary swirl chambers; said nozzle additionally having a spill passage leading to such secondary swirl chamber and effective to bleed a portion of the whirling fuel flowing through such secondary swirl chamber; and a pressure actuated valve in such secondary branch passage effective, when closed, to cut-01f fiow of fuel to such secondary swirl chamber whereby fuel flows exclusively to such primary swirl chamber for discharge through such primary orifice and, when opened, to permit flow of fuel to such secondary swirl chamber whereby fuel flows to such primary and secondary swirl chambers for discharge from such primary and secondary orifices, the discharge from such secondary orifice being regulated by the back pressure in such spill passage.

2. The nozzle of claim 1 wherein said valve is of the pressure-actuated type.

3. The nozzle of claim 1 wherein said valve is of the spring-seated type arranged to be opened responsive to the fuel pressure in such fuel inlet passage reaching a predetermined value.

4. The nozzle of claim 1 wherein said valve is of the pressure-actuated type which, when in closed position, has a primary area thereof exposed to fuel pressure in such fuel inlet passage and which, when in open position, has a substantially larger secondary area exposed to such fuel pressure whereby said valve, once it has been opened by a predetermined fuel pressure acting on such primary area, is kept open by a lower fuel pressure acting on such secondary area.

5'. The nozzle of claim 4 wherein said nozzle has a spring therein that acts on said valve to yield-ably hold it in closed position until the force of the fuel pressure acting on such primary area exceeds the opposing spring force exerted on said valve.

References Cited in the file of this patent UNITED STATES PATENTS 2,315,172 Voorheis Mar. 30, 1943 2,572,606 Fisher Oct. 23, 1951 2,628,867 Purchas Feb. 17, 1953 2,701,164 Purlhas et a1. Feb. 1, 1955 2,703,260 Olson et al Mar. 1, 1955 FOREIGN PATENTS 717,071 Great Britain Oct. 20, 1954 

